A JavaScript developer designs, implements, and maintains websites and software applications using JavaScript, a dynamic programming language. They are responsible for the functionality of the user interface, ensuring optimal performance and user experience. They collaborate with other developers, integrate APIs, debug issues, and optimize code. They also conduct testing, troubleshoot problems, and update software features. Continually learning about new technologies, they often work with frameworks like React or Angular. Their role may also involve backend development using Node.js. To succeed, they need strong problem-solving skills, creativity, and an understanding of web standards and protocols.